1. Field of the Invention
The present invention relates to a compression coding device having a scrambling function, and an expansion reproducing device having a descrambling function. More particularly, the present invention is concerned with a compression coding device adaptive to the MPEG (Moving Picture Experts Group) 2 standard and capable of scrambling and coding data, and an expansion reproducing device also adaptive to the MPEG 2 standard and capable of descrambling and decoding the data scrambled by the coding device.
2. Description of the Background Art
In Japan, for example, scrambled broadcasting using a broadcasting satellite (BS) started in 1991 while broadcasting using a communication satellite (CS) started in 1992 and was scrambled like BS broadcasting. It is a common practice with BS or CS television broadcasting to scramble analog video signals by a line permutation (scanning line transfer) system, line rotation (intra-line signal switching) system, Skyport system, video cypher system, B-MAC system or similar system.
The line permutation system changes the order of scanning lines. The line rotation system provides a cut point or cut points in the individual scanning line and replaces the segments divided by the cut point or points. The Skyport system replaces all the scanning lines at random. The video cypher system removes synchronizing signals from a video signal, and at the same time, reverses the polarity. Further, the B-MAC system varies the length of the individual scanning line at random.
With the advent of full-scale multimedia environments handling speech, data and image (picture) totally, ISO (International Organization for Standardization) is standardizing various kinds of information compression technologies constituting the heart of multimedia. Recently, ISO has standardized MEPG1 as a moving picture coding system for storage and directed toward CD-ROMs (Compact Disk Read Only Memories) and other storage media. Later, ISO has standardized MPEG2 applicable not only to storage media but also to communication and broadcasting media.
A compression coding device adaptive to MPEG2 produces an I picture (Intra-Picture) for a preselected frame or picture of an input moving picture by using, e.g., an intra-frame/intra-field coding system. The coding system produces a P picture (Predictive-Picture) for a single preselected picture different from the I picture by using interframe/interfield forward predictive coding system. Further, the coding system produces a B picture (Bidirectionally Predictive-Picture) for preselected two pictures different from the I and P pictures by using a bidirectionally predictive coding system. The I, P and B pictures, or coded or compressed data, are repeatedly output in the order of, e.g., GOPs (Group-Of-Pictures) shown in FIG. 13B. The coded data output in such an order are, e.g., digitally modulated and broadcast via a BS.
To reproduced the BS broadcast coded data on a monitor, use is made of an expansion reproducing device adaptive to MPEG2. The reproducing device decodes the coded data received from a satellite and transforms the decoded data to a signal which can be displayed by the monitor.
However the problem with the conventional coding device adaptive to MPEG2 is that the coded data are not scrambled despite that the broadcast is chargeable. As a result, any person can decoded the coded data and enjoy a moving picture based on the decoded data on, e.g., a monitor for free only if the person has the expansion reproducing device at hand.